Signaling system



Jan. 6, 1942. w. BUSCHBECKII 8,73

SIGNALING SYSTEM Filed June 27, 1940 I8 3 W1? Z w I: KEYED g": /0 WAVE E 8- INPUT L E E J T E v g INVENTOR WE E B C'HBEC'K BY M1144,

ATTORNEY Patented Jan. 6, 1942v i SIGNALING SYSTEM Werner Buschbeck, Berlin, Germany, asslgnor to Telefunken Gesellscliaft fiir Drahtlose Telegraphic m. b. H., Zehlendorf, Germany, a corporation of Germany Application June 27, 1940, Serial No. 342,631 In Germany January 17, 1939 9 Claims. (Cl. 250-8) This application concerns an arrangement to damp a load circuit in load intervals, particularly for telegraphic signal transmitter circuits. More in detail, this invention is concerned with an arrangement to damp or ballast a load circuit during load intervals of the kind particular- 1y useful for raising the speed of telegraphy using long-wave transmitters comprising lowdamped antenna.

In the case of telegraph signal transmitters designed for long waves the antenna damping only in rare instances is so high that the telegraphic signals will decay within practically negligible lengths of time. But this not only imposes a limitation upon the maximum speed of telegraphic signal transmission, but in addition the attempt to obtain real soft and gentle keying is made substantially more difficult. The instant the master transmitter is cut out, the antenna structure including all circuits ahead of it, for instance, those used for harmonic suppression and the like purposes, is left to itself and the antenna oscillation decays at the frequency or frequencies which result from its tuning. Such decay of the antenna, after disconnection of the master potential in the first place spreads the telegraphic signal to an appreciable extent, and, in the second place, it is liable to vitiate a more or less broad frequency band inasmuch as the natural frequency of the antenna circuit may differ essentially from the master frequency.

Now, the object of the invention is to prevent as far as feasible such slow decay of the antenna oscillation and to insure, on the contrary, damp:

ing that will be initiated practically instantaneously upon disconnection of the master potential. This, for instance, is accomplishable by providing permanently additional damping for the antenna circuit, though this method involves the drawback that essential volumes of energy are thus wasted uselessly while actual key work is proceeding. Another solution would consist of additional damping introduced during the space periods; but such a procedure would be comparatively expensive and complicated.

According to the invention, for the purpose of damping a load circuit during load periods (or spaces) a radio-frequency negative feedback is provided. If for a large penetration factor of the tube in the end or power stage the negative feed-back in the power amplifier circuit is chosen so high that for full grid swing it just attains the size of the control potential (100% negative feedback) then the impulses serving for excitation and damping are of like size.

While it is true that radio-frequency negative feedback is basically known in the art, it serves in the schemes known in the art, for the purpose of precluding distortions, that is, for linearizing the amplifying or modulating characteristic. However, the negative feedback scheme here disclosed differs from the known type of negative feedback insofar as the control or swingin the positive sense always predominates. To be sure,

as a result of the negative feedback, this action will be more or less damped; however, in the case of a telegraphic signal transmitter operating inside the saturation region, this is quite immaterial. The essential effect arises only when the positive control action is totally absent. In fact, what then remains is merely a negative action, and this not even exactly at carrier frequency, but rather at the frequency or frequencies of the free oscillations of the resultant oscillation circuit, line or antenna structure. In other words, the negative feedback in the present instance does not have the effect of improving the linearity of a modulation characteristic, but it rather represents simply an antenna damping which is practically free from frequency effects, that is to say, a damping that becomes operative only at the instant when there is no control potential.

, In order to minimize the loss of gain which occurs in the presence of negative feedback in the power stage, arrangements according to a further object of this invention are made so that the radio-frequency negative feedback is brought back to the grid circuit of an input stage. The greater expenditure of grid power inherent in such a scheme may, as a general rule, be secured without any essential extra cost. For instance, if the input stage which is chosen is a multi-grid type of tube which operates practically without grid current flow, basically only a voltage increase of the grid alternating potential is required without an incidental increase in power expenditure being brought about. The negative feedback potential is preferably introduced in the grid circuit of the last but one stage. What is also essential is that the negative feedback means must be so designed and applied that neutralization will not be endangered as a pended drawing wherein I have illustrated two embodiments of a telegraph signal generator including the new load damping means.

Fig. 1 shows the last two stages of a telegraph-- ic signal transmitter in which all of the circuit elements which are unessential so far as the invention is concerned have been omitted, such as voltage sources of supply, keying devices, etc. The antenna I is fed by way of a coil 2 from the output circuit 3 of the power stage 4. The control grid 8 of this stage 4 is excited by poten tial from the output circuit 5 of the stage preceding the last. The control grid H! of the penultimate stage 6 is excited by control potential from the bridge arrangement l2, the master potential or keyed wave input being impressed to one of the diagonals, a, b, thereof,'while to the other diagonals, c, d, is returned the coupling potential (feedback) from a tap between condensers l4 and I6 of circuit 3. By the adoption of this kind of negative feedback the neutralization of the two tube stages 4 and 6 will not be affected.

Another exemplified embodiment is illustrated in Fig. 2 in which the negative feedback potential is impressed upon a separate grid 18 which is outbalanced and decoupled in respect to the control grid In of the penultimate tube 9. In its essential parts the circuit organization of Fig. 2 is the same as the scheme shown in Fig. 1, identical circuit elements being designated by the same denotations in both arrangements. Tube stage 6 preceding the last, however, comprises here two grids I0 and I8 which are isolatedv by screen grids 20 kept at cathode potential, while the other grid I8 is excited by the negative feedback potential.

This invention is not restricted to telegraph signal transmitter circuit organizations. On the contrary, it will be found useful wherever the point is to damp as instantaneously as possible an oscillatory circuit which is left to itself after disconnection of a control potential, without such damping being liable to produce incidentally an essential efiect upon the oscillation when the radio-frequency potential is operative.

What is claimed is:

1. In a telegraphy system, aplurality of electron discharge tube amplifiers having input and output electrodes connected in high frequency input and output circuits coupling said tubes in cascade, means for impressing keyed high frequency wave energy on the input circuit of the first tube in said cascade, a load coupled to the output circuit of the last tube of said cascade, and means for feeding voltages of the natural frequency of operation of the output circuit of the last tube of said stage degeneratively to an electrode in a tube preceding said last tube during spaces in said high frequency wave energy to damp said system during spaces.

2. A system as recited in claim 1 wherein said last named means comprises a bridge circuit coupled to the input electrodes of said tube preceding said last tube and to the output circuit coupled to said last tube.

3. A system as recited in claim 1 wherein said tube preceding said last tube has an auxiliary electrode shielded from its input electrode and wherein said last means comprises a coupling between the output circuit of the last tube and said auxiliary electrode.

4. In a signaling system, an oscillation circuit for translating radio frequency energy, and means for supplying to said oscillation circuit for translation high frequency oscillations interrupted at signal frequency including, a plurality of tubes having input and output electrodes, a coupling between the output electrodes of one of said tubes and said oscillation circuit, high frequency circuits coupling the input electrodes of said one of said tubes to the output electrodes of another of said tubes, means for impressing interrupted high frequency oscillations on the input electrodes of said other of said tubes, and negative feedback means for damping said oscillation circuit substantially instantly on interruption of said high frequency oscillations without unduly increasing the amount of high frequency energy necessary for driving said tubes, said feedback means including a coupling between the output electrodes of said one said tube and a control electrode of said other tube.

5. A system as recited in claim 4, wherein said last named coupling comprises a bridge circuit having an arm coupled with the input electrodes of said other tube and a diagonal coupled with the output electrode of said one of said tubes.

6. A system as recited in claim 4, wherein said last named coupling includes an additional shielded electrode in said other of said tubes and a coupling between said additional electrode and the output electrodes of said one of said tubes.

'7. In a signaling system, an oscillation circuit for translating radio frequency energy, a load comprising a low damped antenna coupled to said oscillation circuit, and means for supplying to said oscillation circuit for translation high frequency oscillations interrupted at signal frequency comprising, a plurality of tubes having input and output electrodes, a coupling between the output electrodes of'one of said tubes and said oscillation circuit, high frequency circuits coupling the input electrodes of said one of said tubes to the output electrodes of another of said tubes, means for impressing keyed high frequency oscillations on the input electrodes of said other of said tubes, means for neutralizin said one of said tubes, and negative feedback means for damping said oscillation circuit substantially instantly on interruption of said keyed high frequency oscillations without unduly damping said oscillation circuit between interruptions in said impressed high frequency oscillations, said feedback means comprising a coupling between the output electrodes of said one tube and an electrode of said other tube.

8. A system as recited in claim '7, wherein said last named coupling comprises a bridge circuit having an arm coupled to the input electrodes of the other of said tubes and a diagonal coupled to the output electrode of said one of said tubes.

9. A system as recited in claim '7, wherein said last named coupling includes an additional shielded control electrode in said other of saidtubes, coupled to the output electrodes of said one of said tubes.

WERNER 'BUSCHBECK. 

